1. Field of the Invention
The present invention relates to devices, such as catheters, that can be used inside the body for extended periods of time. Several methods are described to facilitate the destruction of bacteria without the necessity of removal of a medical device.
2. Invention Disclosure Statement
Bacteria are present on the surface of the skin and throughout the bodies of humans and animals. Not all of the bacteria are harmful, but medical instruments must be sterilized to prevent harmful bacteria from infecting wounds or incisions. Sterilization before use is sufficient for short-term use instruments, those that remain in contact with the body for less than forty-eight hours, because those medical instruments are generally removed before significant bacterial growth can occur.
Medical devices that remain in the body of humans or animals for longer periods of time create an ideal attachment surface and growth area for bacteria. Furthermore, introduction of medical devices into the body allows bacteria to bypass the subcutaneous layers. The resulting infections can be harmful or even deadly. Current art devices such as catheters can only remain inside the body for a limited amount of time before they must be removed and replaced with a sterilized device. The removal and replacement of these longer-term devices can be complicated and raise the cost of medical care. Removal and replacement is often painful for the patient. Various methods have been proposed to prevent the attachment of bacteria to medical devices as well as destroy bacteria once the device is in the body. One approach has been to incorporate. antibiotics into the medical device materials or onto their surfaces. This method is insufficient because a limited amount of antibiotics can be applied to these surfaces. This limited amount of antibiotic is quickly depleted and used up. Many of the medical devices used in vivo need to remain inside the body for periods of time that are longer than antibiotics can last.
Another approach has been to manufacture the medical device out of a bacteria resistant substance. Along the same line, U.S. Pat. No. 4,476,590 describes an endoprosthetic implant that utilizes an activated silver coating to resist bacteria. One problem that exists with this method is that once the silver coating is activated the effect can not be otherwise controlled. Yet another problem recognized by the above patent is that the silver coating itself may cause damage to connective tissue. The use of a silver coating on medical devices has proved to be mostly unsuccessful in controlling bacterial growth while adding to the cost of manufacturing the medical device.
In a related area of the PDT prior art, U.S. Pat. No. 5,611,793 describes a topical method to disinfect or sterilize tissue in the oral cavity. This method is concerned with disinfecting an accessible area in the mouth and deals strictly with open areas such as wounds or lesions particular to the oral cavity. A photosensitizer, in a solution or gel form, must be applied directly to the sites to be sterilized. The sites are subsequently exposed with a suitable laser light. This method contemplates the use of photosensitizer treatment to sterilize the mouth before surgery, to treat a diagnosed infection, or as a preventative measure for diseases which affect the oral cavity. This is a one-time treatment and the photosensitizer gel or solution must be reapplied whenever sterilization treatment is necessary.
U.S. Pat. No. 5,260,020 describes a catheter that utilizes ultraviolet or infared radiation or other heat producing sources to sterilize the catheter while it remains in vivo. These methods are very non-specific as to its target and could result in the destruction of host cells as well as the targeted bacteria. The ultraviolet radiation proposed is known to kill most living cells, bacteria and host tissue alike. Ultraviolet radiation also has the added problem of an increase in a risk of cancer. Another proposal of xe2x80x98020, is the use of infared radiation to sterilize the catheter. The problem with using infared radiation or the other thermal methods proposed is, that at the intensity level required, damage to surrounding tissue is likely to occur from this prolonged thermal exposure. Conversely, the present invention utilizes a lightsource with a lower intensity and safer wavelength.
It is therefore the goal of the present invention to provide a method to shield/defend medical device surfaces against bacterial growth. The current invention will protect the surfaces of the device for the weeks or months that are frequently required. The problem of bacterial growth on and adherence to medical devices can be overcome by the utilizing the current invention method.
It is an object of the present invention to provide a medical device that will have a reduced possibility of bacterial adherence on its surfaces.
It is also an object of the present invention to provide medical devices that can be kept free of bacteria for extended periods of time during in vivo use.
Another object of the present invention is to provide a method to deter bacterial growth on medical device surfaces by periodically activating a coating, which is capable of inhibiting bacterial growth on the medical device.
It is a further object of the present invention to describe methods to activate a photosensitized coating on a medical device so that the need to remove the device can be avoided.
Briefly stated, the present invention provides a novel approach to fight bacterial growth on and attachment to medical devices. This approach reduces the necessity of the painful and complicated replacement of medical devices that frequently need to remain in the body for periods of time longer than is recommended using a traditionally sterilized device. Several methods are described to kill bacteria that have attached to the surface of medical devices. Long term use is then possible with those medical devices. Furthermore a medical device is described under this method that has a photosensitizing compound affixed to or near the device surface with means to periodically activate the compound by suitable illumination. Several methods are described by which to provide illumination to the photosensitizer near a bacteria growth and attachment site.